Laborer had been shoveling materials most of the day on 5-11-05. At approx 1:30 pm, while shoveling into dumpster box under #4 preheater he alleges feeling a tightness in his lower left back from lifting and twisting. He kept working and reported the incident to the company on 5-12-05 and due to additional soreness on 5-13-05, medical care was provided.